PROJECT SUMMARY This proposal responds to PAR-18-870 titled ?BRAIN Initiative: Development Optimization, and Validation of Novel Tools and Technologies for Neuroscience Research (STTR).? This project is a Fast Track STTR with a phase I and phase II. The small business, Applied Universal Dynamics Corp. (AUD) is collaborating with the University of Minnesota (U of MN). The activity patterns of tens of millions of neurons ? all organized into circuits distributed across multiple brain regions mediate our interaction with the outside world. A mechanistic understanding of the neuronal underpinnings of sensory perception, action, emotion, and cognition requires measuring activities of these neuronal circuits at single cell resolution across several millimeters, and at multiple temporal scales temporal scales. We propose to engineer and commercially disseminate transparent polymer skulls that simultaneously allow wide-field optical neural sensing along with high temporal resolution electrical recordings from the whole mammalian cortex. We will build on key technologies developed in in our laboratories. Specifically, our collaborative has developed a methodology to design and fabricate transparent skulls (Brain Windows) that allow sub-cellular resolution imaging of structure and function of the whole dorsal cortex in behaving mice. In PHASE I of this proposal, we will first utilize 3-dimensional printing methodologies to functionalize these transparent skulls with 8 channels of transparent electrocorticogram (ECoG) recording electrodes (Aim 1). These devices will be utilized to perform simultaneous mesoscale calcium imaging and ECoG recordings (Aim 2). In PHASE II of this proposal, we will refine the 3D printing methodology to realize ultra-high density, transparent 128 channel ?ECoG arrays (Aim 1) for simultaneous whole cortex ECoG and cellular resolution calcium imaging (Aim 2). Finally, we will engineer versions of the technology that allow simultaneous extracellular recordings with surface ECoG and whole cortex optical imaging to realize a platform that allows true 3D brain activity mapping (Aim 3).